An engine that is configured to detect an absolute crank angle (piston position) using a crank angle sensor and a cam angle sensor is known as a conventional internal combustion engine. Specifically, a signal output from the crank angle sensor in accordance with rotation of the crankshaft and a signal output from the cam angle sensor in accordance with rotation of the camshaft are compared, and an absolute crank angle is determined by taking a time point at which a predetermined combination of signal patterns appears as a criterion. According to this method, at startup of the internal combustion engine (at the time of cranking), during a period until the crank angle is determined, more specifically, during a period until the predetermined combination of signal patterns appears, it is necessary for the crankshaft to rotate from approximately 180 to 360°. At the time point at which the crank angle is determined, a cylinder that first enters a compression stroke is distinguished from other cylinders, and fuel injection to the cylinder in question is started.
However, there is a demand to complete cranking in as short a time as possible at startup, to thereby realize favorable startability and suppress power consumption of the battery. Therefore, according to the conventional technology as disclosed, for example, in Patent Literature 1 (Japanese Patent Laid-Open No. 2008-196417), a configuration is adopted that, in order to begin fuel injection at startup earlier than in the above described method, distinguishes a cylinder that is in a compression stroke based on in-cylinder pressures. According to this conventional technology, a cylinder that is in a compression stroke is distinguished based on a pressure difference (ΔP) between in-cylinder pressures at two time points that are separated by a predetermined time period and an amount of change (dP/dt) in the in-cylinder pressure per unit of time.
In addition, as other conventional technology, as disclosed in Patent Literature 2 (Japanese Patent Laid-Open No. 2005-194892), a device is known that is configured to perform cylinder discrimination based on an amount of change (dP/dθ) in an in-cylinder pressure per unit of crank angle. Further, as disclosed in Patent Literature 3 (Japanese Patent Laid-Open No. 2000-64890), a method is known that performs cylinder discrimination at startup using an absolute value of an in-cylinder pressure, and as disclosed in Patent Literature 4 (Japanese Patent Laid-Open No. 2007-291955) a method is also known that determines a crank angle at startup by utilizing a fact that a relation PVκ=constant is established in a cylinder.